Pi calculus is an *(abstract VM) for parallel, mobile computations; for expressing *(concurrency). Its basic version is very low-level, but already universal. _(Higher-order) versions encompass _(lambda calculus).

About Pi-calculus, I've found these pages:
<ul class="links">
<li>_("Calculi for Mobile Processes"|http://move.to/mobility) (_("old"|http://lamp.epfl.ch/mobility/)).
<li>_("Pi-Calculus and Pict"|http://www.cis.upenn.edu/~bcpierce/papers/#Pi-Calculus%20and%20Pict).
<li>There's at least one implemented language based on pi-calculus, _("PICT 4.1"|http://www.cis.upenn.edu/~bcpierce/papers/pict/Html/Pict.html) (also _("here"|http://www.cis.upenn.edu/~bcpierce/papers/pict/)).
</ul>
